Molecules that induce disease resistance in plants

ABSTRACT

Described herein are methods and compositions for enhancing pathogen immunity in plants and improving plant growth.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/205,103, filed Mar. 11, 2014 which claims priority to U.S.Provisional Appl. No. 61/777,957 filed Mar. 12, 2013, the disclosures ofwhich are incorporated by reference herein in its entirety.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH AND DEVELOPMENT

This invention was made with Government support under Grant Nos.DGE0504249 and IOB0449439 awarded by the National Science Foundation.The Government has certain rights in this invention.

BACKGROUND OF THE INVENTION

Plant innate immunity against pathogens depends on a network offunctionally interconnected genes involved in the regulation andexecution of defense reactions (Glazebrook et al. (2003) Plant J.34:217; Tsuda et al. (2009) PLoS Genet. 5:e1000772). A fundamental formof innate immunity in plants involves conserved microbe-associatedmolecular patterns (MAMPs) or general elicitors. MAMPs are recognized bypattern recognition receptors (PRRs) on the surface of plant cells. Uponpathogen recognition, PRRs activate a comprehensive set of defensereactions collectively referred to as pattern triggered immunity (PTI).Some pathogens have independently acquired the ability to evade PTIthrough the release of effector molecules, suppressing defense and thusenabling infection (effector triggered susceptibility, ETS). In thiscase, the pathogen is virulent and the host susceptible. Even in theface of ETS, plants can mount a weakened immune response, called basaldefense, which limits pathogen spread. Basal defense typically cannotfully prevent disease. As a countermeasure to ETS, plants have alsoevolved the ability to recognize the presence of effectors by highlyspecific plant resistance (R) proteins, which mediate effector triggeredimmunity (ETI) resulting in incompatible interactions and leavingpathogens avirulent.

ETI, basal defense, and PTI pathways share some signaling components,such as reactive oxygen species, Ca²⁺, salicylic acid (SA) and jasmonicacid (JA) (Nimchuk et al. (2003) Ann. Rev. Genet. 37:579). The plantimmune system can be subdivided into various defined sectors that caninteract with each other. For example, distinct defense signalingsectors depend on early MAMP-activated MAP kinases or the messengermolecules SA or JA, and some of these sectors can interact in anadditive or synergistic fashion during PTI, or in an antagonistic mannerduring ETI. The latter phenomenon can compensate if a defined sector isdisabled due to interferences with a pathogen effector. A general reviewof chemical defense inducers can be found in Schreiber & Desveaux (2008)Plant Pathology 24:245.

Pesticides are commonly used in agriculture and horticulture for diseasecontrol. Current chemical pesticides, however, typically rely on directantibiotic or biocidal activity, which often leads to undesirable toxicenvironmental side effects. For example, seven of the 10 most frequentlyused pesticides in California tomato production have potential acutetoxic, carcinogenic, neurotoxic or groundwater-contaminating activities,or detrimental effects on human reproduction and development.

BRIEF SUMMARY OF THE INVENTION

Described herein is a class of synthetic elicitors for use inreduced-risk pathogen resistance agents. Without intending to limit theinvention, it is believed that synthetic elicitors fight plant diseasesby enhancing the plant's inherent defense system. The presentlydescribed class of synthetic elicitors have a Phenyl-imino-Methyl-Phenol(PMP) structure.

Provided are compositions having a PMP structure, including those ofFormula I:

or a salt thereof, wherein:R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, and R¹⁰ are each independentlyselected from hydrogen, halogen, hydroxyl, alkoxyl, nitro, substitutedor unsubstituted amino, substituted or unsubstituted alkyl, substitutedor unsubstituted alkenyl, and substituted or unsubstituted carbonyl.Such compounds, when contacted with a plant, increase pathogenresistance of the plant compared to pathogen resistance of a controlplant not contacted with the compound.

In some embodiments, R¹ is hydrogen, hydroxyl, or part of an aryl (e.g.,phenyl) group with R². In some embodiments, R² is hydrogen, halide(e.g., Cl, Br, I), or part of an aryl (e.g., phenyl) group with R¹. Insome embodiments, R³ is hydrogen or halide (e.g., Cl, Br, I). In someembodiments, R⁴ is hydrogen, halide (e.g., Cl, Br, I), or nitro. In someembodiments, R⁵ is hydrogen or hydroxyl. In some embodiments, R⁶ ishydrogen, halide (e.g., Cl, Br, I), hydroxyl, or alkyl (e.g., methyl).In some embodiments, R⁷ is hydrogen, methoxy, amide, or halide (e.g.,Cl, Br, I). In some embodiments, R⁸ is hydrogen, methylacetamide, amine,methyl, or halide (e.g., Cl, Br, I). In some embodiments, R⁹ ishydrogen, acetamide, tert-butyl, or halide (e.g., Cl, Br, I). In someembodiments, R¹⁰ is hydrogen or halide (e.g., Cl, Br, I). In someembodiments, the compound is selected from the group consisting of:

Further provided is an agricultural composition comprising the compoundas described above formulated for application to a plant or plant part.In some embodiments, the agricultural composition also comprises atleast one of an herbicide, an herbicide safener, a surfactant, afungicide, a pesticide, a nematicide, a plant activator, a synergist, aplant growth regulator, an insect repellant, an acaricide, amolluscicide, or a fertilizer. In some embodiments, the agriculturalcomposition is formulated for spraying or soaking. In some embodiments,the agricultural composition is formulated in a dry form, e.g., fordusting or soil application. In some embodiments, the agriculturalcomposition is formulated in a dried or concentrated form to berehydrated or diluted before application.

Further provided are methods of increasing pathogen resistance in aplant, comprising contacting (or applying to) the plant an effectiveamount of a compound as described above, e.g., in an agriculturalcomposition, wherein the compound increases pathogen resistance in theplant compared to pathogen resistance in a plant not treated with thecompound (e.g., an untreated control plant, or the same plant prior tocontacting). In some embodiments, the compound increases pathogenresistance by at least 10, 20, 30, 40, 50, 60, 70, 80, 90, or 100% ormore, e.g., as measured by increased pathogen response gene expressionor by reduction in pathogen amount, number, or effect. In someembodiments, the compound reduces the amount or number of pathogen, orreduces the effect of pathogen, at least 1.5-fold, 2-fold, 3-fold,5-fold, 10-fold or more. In some embodiments, the compound is applied ata concentration of 0.05-200 uM, 0.1-100 uM, 0.1-50 uM, 0.5-10 uM, 0.5uM, 1 uM, 5 uM, 10 uM, 25 uM, or 50 uM. In some embodiments, thecompound is applied more than once, e.g., at least 2, 3, 4, 5, 6, 7, 8,9, or 10 times. In some embodiments, the compound is applied every 8hours, twice daily, daily, every other day, twice weekly, etc. In someembodiments, the compound is contacted with a plant where the pathogenis already present. In some embodiments, the compound is contacted witha plant that is not affected by pathogen. In some embodiments, themethod further comprises detecting the amount, number or effect ofpathogen before contacting, and in some embodiments, further comprisesdetecting the amount, number or effect of pathogen after contacting oneor more times. In some embodiments, the compound is contacted with theplant until the pathogen is not detectable, or is detectable at a levelthat does not affect the plant.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. Phenyl-imino-methyl-phenol derivatives (PMPs) constitute a largeclass of new synthetic elicitors. A: Structures of 20 PMP derivativesthat were identified by high throughput screening as able to promoteexpression with the CaBP22 reporter assay. B. CMP199 was furtheranalyzed in the Noco2 spore inhibition assay. Three-week-old soil-grownCol-0 seedlings were spray-infected 24 h after treating with varyingconcentrations of each synthetic elicitor and then assayed at 7 dpi forspore growth. 100% inhibition=0 spores. The assay was repeated threetimes with similar results, and the average of those three replicates isshown. DCA=3-5-dicholoroanthranlilic acid;HTC=2-(5-bromo-2-hydroxy-phenyl)-thiazolidine-4-carboxylic acid.

DETAILED DESCRIPTION OF THE INVENTION I. Introduction

Synthetic elicitors are drug-like compounds that induce the plantnatural immune response to pathogen. Synthetic elicitors need not betoxic for pathogenic organisms, which allows for production of apathogen defense treatment that is less harmful to humans and theenvironment. Using high-throughput chemical screening, we identified aclass of synthetic elicitor candidates that activate expression of thepathogen-responsive CaBP22⁻³³³:GUS reporter gene in transgenicArabidopsis thaliana plants. This class is characterized by aPhenyl-imino-methyl-phenol (PMP) structure. One of these compounds,2,4-dichloro-6-[((3-methoxy-phenyl) imino) methyl]-phenol (CMP199), isable to induce disease resistance in A. thaliana at very lowconcentration, and is structurally distinct from other known plantdefense inducing chemicals. Accordingly, provided herein is a class ofstructurally related compounds that can improve plant pathogenresistance.

II. Definitions

An “agricultural composition” is a composition formulated forapplication to a plant or plant part (e.g., seed, cutting, shoots,etc.). An agricultural composition is typically in liquid form, e.g.,for application by spraying or soaking, but can be in a powder forrehydration or application (dusting or dry coating), or gaseous form(e.g., for enclosed environments). The agricultural composition can beconcentrated, e.g., for dilution or water or other solvent. Anagricultural composition can also include more than one activeingredient, e.g., an HTC class compound in combination with a fungicide,herbicide, fertilizer, etc.

The terms “increase pathogen resistance,” “enhance plant immunity,”“promote disease resistance,” “induce plant pathogen defense,” “improveimmunity to pathogens,” and like terms refer to the ability of asubstance to protect a plant from pathogen infection or infestation. Theincrease in protective effect is typically determined by comparison to acontrol. An agent or composition that increases pathogen resistancetypically reduces the number/amount of pathogen affecting a plant at agiven time post-infection by at least 1.5-fold, e.g., 2-fold, 3-fold,5-fold, 10-fold, or more (or by 20%, 40%, 50%, 70%, 80%, 90% or more)compared to control not treated with the agent or composition.Alternatively, an increase in pathogen resistance can be measured inexpression of pathogen-resistance genes (e.g., CaBP22, etc.) in anaffected plant. An agent or composition that increases pathogenresistance can lead to an increase of a pathogen resistance gene by atleast 1.5-fold, e.g., 2-fold, 3-fold, 5-fold, 10-fold, or more (or by25%, 50%, 75%, 100% or more) compared to control not treated with theagent or composition. Pathogen resistance can also be determined byobserving plant survival time, physical effects of pathogen invasion(e.g., lesions, stunted or abnormal growth, etc.).

The terms “increase growth,” “improve growth,” “enhance growth,”“promote growth,” “induce growth,” and like terms refer to the abilityof a substance to speed up growth of a plant or plant structure over agiven time span, typically as compared to a control. An agent orcomposition that increases growth typically increases the size or weightof a given plant structure, at a given time, by at least 10%, 20%, 40%,50%, 70%, 80%, 90% or more compared to control not treated with theagent or composition.

A “control” sample or value refers to a sample that serves as areference, usually a known reference, for comparison to a test sample.For example, a test sample can be taken from a test condition, e.g., inthe presence of a test compound, and compared to samples from knownconditions, e.g., in the absence of the test compound (negativecontrol), or in the presence of a compound known to have the desiredeffect (positive control). A control can also represent an average valuegathered from a number of tests or results. One of skill in the art willrecognize that controls can be designed for assessment of any number ofparameters. For example, a control can be devised to compare benefit,e.g., for peripheral composition considerations (e.g., half-life,adhesiveness) or for measures of the desired activity (e.g., comparisonof pathogen resistance, growth, and/or side effects). Controls can bedesigned for in vitro applications, e.g., using reporter gene assays.One of skill in the art will understand which controls are valuable in agiven situation and be able to analyze data based on comparisons tocontrol values. Controls are also valuable for determining thesignificance of data. For example, if values for a given parameter varyin controls, variation in test samples will not be considered assignificant.

Examples of negative controls in the context of the present disclosureinclude plants that are not treated with a particular composition, aplant before treatment, an average value of similar plants grown insimilar but untreated conditions. Examples of positive controls includeplants that are genetically modified for pathogen resistance, plantstreated with a substance that is known to be toxic to the pathogen inquestion or known to increase pathogen resistance in a plant. One ofskill in the art will understand how to select an appropriate controlfor a given condition.

“Alkyl” refers to a straight or branched, saturated, aliphatic radicalhaving the number of carbon atoms indicated. Alkyl can include anynumber of carbons, such as C₁₋₂, C₁₋₃, C₁₋₄, C₁₋₅, C₁₋₆, C₁₋₇, C₁₋₈,C₁₋₉, C₁₋₁₀, C₂₋₃, C₂₋₄, C₂₋₅, C₂₋₆, C₃₋₄, C₃₋₅, C₃₋₆, C₄₋₅, C₄₋₆ andC₅₋₆. For example, C₁₋₆ alkyl includes, but is not limited to, methyl,ethyl, propyl, isopropyl, butyl, isobutyl, sec_butyl, tert_butyl,pentyl, isopentyl, hexyl, etc. Alkyl can also refer to alkyl groupshaving up to 20 carbons atoms, such as, but not limited to heptyl,octyl, nonyl, decyl, etc. Alkyl groups can be substituted orunsubstituted.

“Alkylene” refers to a straight or branched, saturated, aliphaticradical having the number of carbon atoms indicated, and linking atleast two other groups, i.e., a divalent hydrocarbon radical. The twomoieties linked to the alkylene can be linked to the same atom ordifferent atoms of the alkylene group. For instance, a straight chainalkylene can be the bivalent radical of —(CH₂)_(n)—, where n is 1, 2, 3,4, 5 or 6. Representative alkylene groups include, but are not limitedto, methylene, ethylene, propylene, isopropylene, butylene, isobutylene,sec-butylene, pentylene and hexylene. Alkylene groups can be substitutedor unsubstituted.

“Alkenyl” refers to a straight chain or branched hydrocarbon having atleast 2 carbon atoms and at least one double bond. Alkenyl can includeany number of carbons, such as C₂, C₂₋₃, C₂₋₄, C₂₋₅, C₂₋₆, C₂₋₇, C₂₋₈,C₂₋₉, C₂₋₁₀, C₃, C₃₋₄, C₃₋₅, C₃₋₆, C₄, C₄₋₅, C₄₋₆, C₅, C₅₋₆, and C₆.Alkenyl groups can have any suitable number of double bonds, including,but not limited to, 1, 2, 3, 4, 5 or more. Examples of alkenyl groupsinclude, but are not limited to, vinyl (ethenyl), propenyl, isopropenyl,1-butenyl, 2-butenyl, isobutenyl, butadienyl, 1-pentenyl, 2-pentenyl,isopentenyl, 1,3-pentadienyl, 1,4-pentadienyl, 1-hexenyl, 2-hexenyl,3-hexenyl, 1,3-hexadienyl, 1,4-hexadienyl, 1,5-hexadienyl,2,4-hexadienyl, or 1,3,5-hexatrienyl. Alkenyl groups can be substitutedor unsubstituted.

“Alkoxy” refers to an alkyl group having an oxygen atom that connectsthe alkyl group to the point of attachment: alkyl-O—. As for alkylgroup, alkoxy groups can have any suitable number of carbon atoms, suchas C₁₋₆. Alkoxy groups include, for example, methoxy, ethoxy, propoxy,iso-propoxy, butoxy, 2-butoxy, iso-butoxy, sec-butoxy, tert-butoxy,pentoxy, hexoxy, etc. The alkoxy groups can be further substituted witha variety of substituents described within. Alkoxy groups can besubstituted or unsubstituted.

“Amine” refers to an —N(R)₂ group where the R groups can be hydrogen,alkyl, alkenyl, alkynyl, cycloalkyl, heterocycloalkyl, aryl, orheteroaryl, among others. The R groups can be the same or different. Theamino groups can be primary (each R is hydrogen), secondary (one R ishydrogen) or tertiary (each R is other than hydrogen).

“Aryl” refers to an aromatic ring system having any suitable number ofring atoms and any suitable number of rings. Aryl groups can include anysuitable number of ring atoms, such as, 6, 7, 8, 9, 10, 11, 12, 13, 14,15 or 16 ring atoms, as well as from 6 to 10, 6 to 12, or 6 to 14 ringmembers. Aryl groups can be monocyclic, fused to form bicyclic ortricyclic groups, or linked by a bond to form a biaryl group.Representative aryl groups include phenyl, naphthyl and biphenyl. Otheraryl groups include benzyl, having a methylene linking group. Some arylgroups have from 6 to 12 ring members, such as phenyl, naphthyl orbiphenyl. Other aryl groups have from 6 to 10 ring members, such asphenyl or naphthyl. Some other aryl groups have 6 ring members, such asphenyl. Aryl groups can be substituted or unsubstituted.

“Heterocycloalkyl” refers to a saturated ring system having from 3 to 12ring members and from 1 to 4 heteroatoms of N, O and S. Additionalheteroatoms can also be useful, including, but not limited to, B, Al, Siand P. The heteroatoms can also be oxidized, such as, but not limitedto, —S(O)— and —S(O)₂—. Heterocycloalkyl groups can include any numberof ring atoms, such as, 3 to 6, 4 to 6, 5 to 6, 3 to 8, 4 to 8, 5 to 8,6 to 8, 3 to 9, 3 to 10, 3 to 11, or 3 to 12 ring members. Any suitablenumber of heteroatoms can be included in the heterocycloalkyl groups,such as 1, 2, 3, or 4, or 1 to 2, 1 to 3, 1 to 4, 2 to 3, 2 to 4, or 3to 4. The heterocycloalkyl group can include groups such as aziridine,azetidine, pyrrolidine, piperidine, azepane, azocane, quinuclidine,pyrazolidine, imidazolidine, piperazine (1,2-, 1,3- and 1,4-isomers),oxirane, oxetane, tetrahydrofuran, oxane (tetrahydropyran), oxepane,thiirane, thietane, thiolane (tetrahydrothiophene), thiane(tetrahydrothiopyran), oxazolidine, isoxazolidine, thiazolidine,isothiazolidine, dioxolane, dithiolane, morpholine, thiomorpholine,dioxane, or dithiane. The heterocycloalkyl groups can also be fused toaromatic or non-aromatic ring systems to form members including, but notlimited to, indoline. Heterocycloalkyl groups can be unsubstituted orsubstituted. For example, heterocycloalkyl groups can be substitutedwith C₁₋₆ alkyl or oxo (═O), among many others.

The heterocycloalkyl groups can be at any position on the ring. Forexample, aziridine can be 1- or 2-aziridine, azetidine can be 1- or2-azetidine, pyrrolidine can be 1-, 2- or 3-pyrrolidine, piperidine canbe 1-, 2-, 3- or 4-piperidine, pyrazolidine can be 1-, 2-, 3-, or4-pyrazolidine, imidazolidine can be 1-, 2-, 3- or 4-imidazolidine,piperazine can be 1-, 2-, 3- or 4-piperazine, tetrahydrofuran can be 1-or 2-tetrahydrofuran, oxazolidine can be 2-, 3-, 4- or 5-oxazolidine,isoxazolidine can be 2-, 3-, 4- or 5-isoxazolidine, thiazolidine can be2-, 3-, 4- or 5-thiazolidine, isothiazolidine can be 2-, 3-, 4- or5-isothiazolidine, and morpholine can be 2-, 3- or 4-morpholine.

When a heterocycloalkyl includes 3 to 8 ring members and 1 to 3heteroatoms, representative members include, but are not limited to,pyrrolidine, piperidine, tetrahydrofuran, oxane, tetrahydrothiophene,thiane, pyrazolidine, imidazolidine, piperazine, oxazolidine,isoxzoalidine, thiazolidine, isothiazolidine, morpholine,thiomorpholine, dioxane and dithiane. Heterocycloalkyl can also form aring having 5 to 6 ring members and 1 to 2 heteroatoms, withrepresentative members including, but not limited to, pyrrolidine,piperidine, tetrahydrofuran, tetrahydrothiophene, pyrazolidine,imidazolidine, piperazine, oxazolidine, isoxazolidine, thiazolidine,isothiazolidine, and morpholine.

“Heterocyclalkylene” refers to a heterocyclalkyl group, as definedabove, linking at least two other groups. The two moieties linked to theheterocyclalkylene can be linked to the same atom or different atoms ofthe heterocyclalkylene. Heterocycloalkylene groups can be substituted orunsubstituted. As used herein, the term unsubstituted indicates theheterocycloalkyl has a full complement of hydrogens, i.e., commensuratewith its saturation level, with no substitutions, e.g., linear decane(—(CH₂)₉—CH₃).

The term “halide” or “halogen” refers to the fluorine, chlorine,bromine, and iodine.

The term “hydroxyl” as used herein is represented by the formula —OH.

The term nitro as used herein is represented by the formula —NO₂.

Unless stated to the contrary, a formula with chemical bonds shown onlyas solid lines and not as wedges or dashed lines contemplates eachpossible isomer, e.g., each enantiomer, diastereomer, and meso compound,and a mixture of isomers, such as a racemic or scalemic mixture.

The term “plant” includes whole plants, shoot vegetativeorgans/structures (e.g., leaves, stems and tubers), roots, flowers andfloral organs/structures (e.g., bracts, sepals, petals, stamens,carpels, anthers and ovules), seed (including embryo, endosperm, andseed coat) and fruit (the mature ovary), plant tissue (e.g., vasculartissue, ground tissue, and the like) and cells (e.g., guard cells, eggcells, and the like), and progeny of same. Plants that can be treated asdescribed herein include angiosperms (monocotyledonous anddicotyledonous plants), gymnosperms, ferns, horsetails, psilophytes,lycophytes, bryophytes, and multicellular algae.

The term “plant” also includes naturally-occurring mutants,genetically-modified plants, and transgenic plants. A“genetically-modified plant” is one whose genome has been manipulated sothat it is different than a wild-type plant of the same species, varietyor cultivar, e.g., to add a gene or genetic element, remove a gene orgenetic element, change chromatin structure, change RNA expressionlevels, etc. Genetically-modified plants include transgenic plants. A“transgenic plant” refers to a plant that contains genetic material notfound in a wild-type plant of the same species, variety or cultivar. Thegenetic material can include a transgene, a reporter construct, aninsertional mutagenesis event (such as by transposon or T-DNAinsertional mutagenesis), an activation tagging sequence, a mutatedsequence, a homologous recombination event or a sequence modified bychimeraplasty. A transgenic plant may contain an expression vector orcassette. The expression cassette typically comprises apolypeptide-encoding sequence or a modulating nucleic acid (e.g., anantisense, an siRNA or ribozyme) operably linked (i.e., under regulatorycontrol of) to an appropriate inducible or constitutive regulatorysequences that allow for the expression of a polypeptide or modulatingnucleic acid. The expression cassette can be introduced into a plant bytransformation or by breeding after transformation of a parent plant.Such methods can be used in a whole plant, including seedlings andmature plants, as well as to a plant part, such as seed, fruit, leaf, orroot, plant tissue, plant cells or any other plant material, e.g., aplant explant, as well as to progeny thereof, and to in vitro systemsthat mimic biochemical or cellular components or processes in a cell.For example, in one embodiment, the disclosure provides an expressioncassette comprising a pathogen response gene (e.g., CaBP22) promoterregion operably linked to a heterologous polynucleotide, e.g., todetermine if a given compound activates pathogen resistance pathways ina plant. The expression cassette can be used in an expression system,whereby induction of transcription by the promoter can be induced bycontact with a compound of Formula I. Accordingly, transgenic plantscomprising an expression cassette of the disclosure can be induced toexpress a desired gene or polynucleotide upon contact with a compound ofFormula I.

III. Plants and Plant Pathogens

The presently described compounds can be effective for enhancingpathogen immunity and stimulating growth in a broad range of plants,e.g., dicots or monocots, and plants used for food, fiber, or energyproduction. Exemplary plant species include but are not limited tospecies from the genera Asparagus, Atropa, Avena, Brassica, Citrus,Citrullus, Capsicum, Cucumis, Cucurbita, Daucus, Fragaria, Glycine,Gossypium, Helianthus, Heterocallis, Hordeum, Hyoscyamus, Lactuca,Linum, Lolium, Lycopersicon, Malta, Manihot, Majorana, Medicago,Nicotiana, Oryza, Panieum, Pannesetum, Persea, Pisum, Pyrus, Prunus,Raphanus, Secale, Senecio, Sinapis, Solanum, Sorghum, Trigonella,Triticum, Vitis, Vigna, and, Zea. In some embodiments, the plant is anornamental plant. In some embodiments, the plant is a vegetable- orfruit-producing plant, e.g., tomato, strawberry, fruit tree, etc. Insome embodiments, the presently described compounds are applied to aplant selected from: apple, apricot, avocado, banana, blueberry,boysenberry, Brassicacea crop (e.g., cabbage, cauliflower, rape),carrot, citrus (e.g., orange, tangerine, lemon, grapefruit), cereal crop(e.g., rice, maize, wheat, barley, millet, sorghum, oats, triticale,rye), non-cereal grasses (e.g., bamboo, switch grass), cherry, date,fig, grape, kiwifruit, legume crop (e.g., bean, soybean, pea, cowpea,lentil), marijuana, nectarine, nut, olive, peach, pear, plum, raspberry,solanecea crop (e.g., tobacco, tomato, pepper, potato), strawberry,sugarbeet, sugarcane, and wood crops (e.g., birch, pine, poplar, oak,etc.).

Those of skill will recognize that a number of plant species can be usedas models to predict the effects of the presently described compounds inother plants. For example, it is well recognized that tomato (Solanum),tobacco (Nicotiana) and Arabidopsis plants are useful models, e.g. forother dicots, and Zea can be a useful model for monocots in particular.

The presently described compounds enhance the immune response of thetreated plant, and thus are effective against a variety of plantpathogens, such as, but not limited to, Colletotrichum graminocola,Diplodia maydis, Verticillium dahliae, Fusarium graminearum, Fusariumoxysporum and Fusarium verticillioides. The presently disclosedcompounds can be used to address pathogens that affect major crops,including: Soybeans: Phytophthora megasperma fsp. glycinea, Macrophominaphaseolina, Rhizoctonia solani, Sclerotinia sclerotiorum, Fusariumoxysporum, Diaporthe phaseolorum var. sojae (Phomopsis sojae), Diaporthephaseolorum var. caulivora, Sclerotium rolfsii, Cercospora kikuchii,Cercospora sojina, Peronospora manshurica, Colletotrichum dematium(Colletotichum truncatum), Corynespora cassuicola, Septoria glycines,Phyllosticta sojicola, Alternaria alternata, Pseudomonas syringae p.v.glycinea, Xanthomonas campestris p.v. phaseoli, Microsphaera diffusa,Fusarium semitectum, Phialophora gregata, Glomerella glycines,Phakopsora pachyrhizi, Pythium aphanidermatum, Pythium ultimum, Pythiumdebaryanum, Fusarium solani; Canola: Albugo candida, Alternariabrassicae, Leptosphaeria maculans, Rhizoctonia solani, Sclerotiniasclerotiorum, Mycosphaerella brassicicola, Pythium ultimum, Peronosporaparasitica, Fusarium roseum, Alternaria alternata; Alfalfa: Clavibactermichiganese subsp. insidiosum, Pythium ultimum, Pythium irregulare,Pythium splendens, Pythium debaryanum, Pythium aphanidermatum,Phytophthora megasperma, Peronospora trifoliorum, Phoma medicaginis var.medicaginis, Cercospora medicaginis, Pseudopeziza medicaginis,Leptotrochila medicaginis, Fusarium oxysporum, Verticillium albo-atrum,Xanthomonas campestris p.v. alfalfae, Aphanomyces euteiches, Stemphyliumherbarum, Stemphylium alfalfae, Colletotrichum trifolii,Leptosphaerulina briosiana, Uromyces striates, Sclerotinia trifoliorum,Stagonospora meliloti, Stemphylium botryosum, Leptotrichila medicaginis;Wheat: Pseudomonas syringae p.v. atrofaciens, Urocystis agropyri,Xanthomonas campestris p.v. translucens, Pseudomonas syringae p.v.syringae, Alternaria alternata, Cladosporium herbarum, Fusariumgraminearum, Fusarium avenaceum, Fusarium culmorum, Ustilago tritici,Ascochyta tritici, Cephalosporium gramineum, Collotetrichum graminicola,Erysiphe graminis fsp. tritici, Puccinia graminis fsp. tritici, Pucciniarecondita fsp. tritici, Puccinia striiformis, Pyrenophoratritici-repentis, Septoria nodorum, Septoria tritici, Septoria avenae,Pseudocercosporella herpotrichoides, Rhizoctonia solani, Rhizoctoniacerealis, Gaeumannomyces graminis var. tritici, Pythium aphanidermatum,Pythium arrhenomanes, Pythium ultimum, Bipolaris sorokiniana, Clavicepspurpurea, Tilletia tritici, Tilletia laevis, Ustilago tritici, Tilletiaindica, Rhizoctonia solani, Pythium arrhenomannes, Pythium gramicola,Pythium aphanidermatum; Sunflower: Plasmopora halstedii, Sclerotiniasclerotiorum, Septoria helianthi, Phomopsis helianthi, Alternariahelianthi, Alternaria zinniae, Botrytis cinerea, Phoma macdonaldii,Macrophomina phaseolina, Erysiphe cichoracearum, Rhizopus oryzae,Rhizopus arrhizus, Rhizopus stolonifer, Puccinia helianthi, Verticilliumdahliae, Erwinia carotovorum pv. carotovora, Cephalosporium acremonium,Phytophthora cryptogea, Albugo tragopogonis; Corn: Colletotrichumgraminicola, Fusarium verticillioides var. subglutinans, Erwiniastewartii, F. verticillioides, Gibberella zeae (Fusarium graminearum),Stenocarpella maydi (Diplodia maydis), Pythium irregulare, Pythiumdebaryanum, Pythium graminicola, Pythium splendens, Pythium ultimum,Pythium aphanidermatum, Aspergillus flavus, Bipolaris maydis O, T(Cochliobolus heterostrophus), Helminthosporium carbonum I, II & III(Cochliobolus carbonum), Exserohilum turcicum I, II & III,Helminthosporium pedicellatum, Physoderma maydis, Phyllosticta maydis,Kabatiella maydis, Cercospora sorghi, Ustilago maydis, Puccinia sorghi,Puccinia polysora, Macrophomina phaseolina, Penicillium oxalicum,Nigrospora oryzae, Cladosporium herbarum, Curvularia lunata, Curvulariainaequalis, Curvularia pallescens, Clavibacter michiganense subsp.nebraskense, Trichoderma viride, Claviceps sorghi, Pseudomonas avenae,Erwinia chrysanthemi pv. zea, Erwinia carotovora, Corn stuntspiroplasma, Diplodia macrospora, Sclerophthora macrospora,Peronosclerospora sorghi, Peronosclerospora philippinensis,Peronosclerospora maydis, Peronosclerospora sacchari, Sphacelothecareiliana, Physopella zeae, Cephalosporium maydis, Cephalosporiumacremonium; Sorghum: Exserohilum turcicum, C. sublineolum, Cercosporasorghi, Gloeocercospora sorghi, Ascochyta sorghina, Pseudomonas syringaep.v. syringae, Xanthomonas campestris p.v. holcicola, Pseudomonasandropogonis, Puccinia purpurea, Macrophomina phaseolina, Perconiacircinata, Fusarium verticillioides, Alternaria alternata, Bipolarissorghicola, Helminthosporium sorghicola, Curvularia lunata, Phomainsidiosa, Pseudomonas avenae (Pseudomonas alboprecipitans), Ramulisporasorghi, Ramulispora sorghicola, Phyllachara sacchari, Sporisoriumreilianum (Sphacelotheca reiliana), Sphacelotheca cruenta, Sporisoriumsorghi, Claviceps sorghi, Rhizoctonia solani, Acremonium strictum,Sclerophthona macrospora, Peronosclerospora sorghi, Peronosclerosporaphilippinensis, Sclerospora graminicola, Fusarium graminearum, Fusariumoxysporum, Pythium arrhenomanes, Pythium graminicola, etc.

IV. Compounds

A class of synthetic elicitors useful in the methods described hereinincludes compounds represented by Formula I:

or a salt thereof.

In Formula I, R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, and R¹⁰ are eachindependently selected from hydrogen, halogen, hydroxyl, alkoxyl, nitro,substituted or unsubstituted amino, substituted or unsubstituted alkyl,substituted or unsubstituted alkenyl, and substituted or unsubstitutedcarbonyl. In Formula I, adjacent R groups (e.g., R¹ and R², R² and R³,R³ and R⁴, R⁴ and R⁵, R⁶ and R⁷, R⁷ and R⁸, R⁸ and R⁹, or R⁹ and R¹⁰)can be combined to form a substituted or unsubstituted aryl or asubstituted or unsubstituted heteroaryl. For example, R⁴ can be asubstituted or unsubstituted ethylene group and R⁵ can be a substitutedor unsubstituted propylene group that combine to form a substituted orunsubstituted phenyl.

Optionally, R¹ is hydrogen, hydroxyl, or part of a phenyl group with R².Optionally, R² is hydrogen, halide (e.g., Cl, Br), or part of a phenylgroup with R¹. Optionally, R³ is hydrogen or halide (e.g., Cl).Optionally, R⁴ is hydrogen, halide (e.g., Cl, Br), or nitro. Optionally,R⁵ is hydrogen or hydroxyl. Optionally, R⁶ is hydrogen, halide (e.g.,Cl), hydroxyl, or alkyl (e.g., methyl). Optionally, R⁷ is hydrogen,methoxy, amide, or halide (e.g., Cl, I). Optionally, R⁸ is hydrogen,halide (e.g., Cl), methylacetamide, amine, alkyl (e.g., methyl).Optionally, R⁹ is hydrogen, acetamide, alkyl (e.g., tert-butyl), orhalide (e.g., Cl). Optionally, R¹⁰ is hydrogen or halide (e.g., Cl)

Examples of Formula I include the following compounds:

The compounds described herein include those with aphenyl-imino-methyl-pheno (PMP) skeleton. In some cases, the compoundsare commercially available (e.g., from Sigma-Aldrich®/TimTec®), or canbe prepared using synthetic methods known in the art. The compoundsdescribed herein can be prepared from readily available startingmaterials. Optimum reaction conditions may vary with the particularreactants or solvent used, but such conditions can be determined by oneskilled in the art by routine optimization procedures.

Variations on Formula I include the addition, subtraction, or movementof the various constituents as described for each compound. Similarly,when one or more chiral centers is present, the chirality of themolecule can be changed. Additionally, compound synthesis can involvethe protection and deprotection of various chemical groups. The use ofprotection and deprotection, and the selection of appropriate protectinggroups can be readily determined by one skilled in the art. Thechemistry of protecting groups can be found, for example, in Wuts andGreene, Protective Groups in Organic Synthesis, 4^(th) Ed., Wiley &Sons, 2006. Testing of synthesized compounds of Formula I can be carriedout using reporter assays or pathogen protection assays, e.g., asdescribed in the Examples.

Reactions to produce the compounds described herein can be carried outin one or more solvents, which can be readily selected by one of skillin the art of organic synthesis. Solvents can be substantiallynonreactive with the starting materials (reactants), the intermediates,or products under the conditions at which the reactions are carried out,i.e., temperature and pressure. Product or intermediate formation can bemonitored according to any suitable method, e.g., by spectroscopicmeans, such as nuclear magnetic resonance spectroscopy (e.g., ¹H or ¹³C)infrared spectroscopy, spectrophotometry (e.g., UV-visible), or massspectrometry, or by chromatography such as high performance liquidchromatography (HPLC) or thin layer chromatography.

Compounds according to Formula I can be prepared, e.g., as described inScheme 1.

As shown in Scheme 1, the compound according to Formula I can be made,for example, by refluxing aldehyde (1) and aniline (2) in a solvent(e.g., ethanol) to form the compound according to Formula I.

In some embodiments, the disclosure provides compositions for protectinga plant from a pathogen comprising an effective amount of at least onecompound of Formula I. In some embodiments, the application of thecomposition increases the expression of a plant pathogen responsive gene(e.g., CaBP22). “Effective amount” is intended to mean a compound orcomposition sufficient to reduce pathogen survival or growth, e.g., by10%, 20%, 50%, 75%, 80%, 90%, 95%, or more compared to a negativecontrol. In some embodiments, the effective amount of a compound ofFormula I for protecting a plant from a pathogen is 0.05-250 uM, 0.1-200uM, 0.1-100 uM, 0.5-100 uM, 10-100 uM, 0.5-50 uM, or 25-75 uM. Acompound of the disclosure can be applied to a plant or plant part,e.g., the environment of the pathogen, by methods known to those ofordinary skill in the art.

V. Methods of Screening

Provided herein are methods to determine whether, and to what extent, aPMP compound (e.g., a compound of Formula I or a compound with aphenyl-imino-methyl phenol derivative structure) can be used to increasepathogen resistance or increase plant growth.

Assays for determining pathogen resistance are described herein, andinclude reporter assays, e.g., using a reporter construct comprising aregulatory region from a pathogen resistance gene (e.g. a gene on asalicylic acid-dependent or -independent pathway, a gene on the jasmonicacid-dependent or -independent pathway, or as described in Knoth et al.(2009) Plant Physiol. 150:333) operatively linked to a reporter (e.g.,GFP, luciferase, or other detectable marker). Pathogen resistance canalso be tested in situ, e.g., by contacting a plant with a pathogen inthe presence or absence (negative control) of a test compound (e.g., aPMP compound), and determining the pathogen protecting ability of thetest compound by measuring the number or amount of the pathogen, or theeffect of the pathogen on the plant (e.g., lesions, or reduced plantsurvival). The pathogen can be contacted with the plant at the sametime, before, or after the test compound. In some embodiments, the plantis contacted with the test compound before and after contact with thepathogen. In some embodiments, the plant is contacted with the pathogenand/or test compound is contacted with the plant more than once, e.g.,to determine the duration of efficacy of the compound. The assay canalso include a positive control, e.g., a plant contacted with CMP199. Areduced number, amount, or effect of pathogen compared to a negativecontrol indicates the test compound increases pathogen resistance. Oneof skill will appreciate that methods of screening a PMP compound forits pathogen protecting activity can be adjusted, e.g., efficacy can bemeasured in different ways depending on the effect of the pathogen onthe plant of interest. In addition, a plant tissue can be used insteadof a whole plant. In some embodiments, the plant is agenetically-modified plant, e.g., a plant with a mutation in a pathogensignaling pathway (see, e.g., Lu (2009) Plant Signal Behav. 4:713).

VI. Agricultural Compositions

An agricultural composition comprising a compound of Formula I can alsoinclude one or more of: a surface-active agent, an inert carrier, apreservative, a humectant, a feeding stimulant, an attractant, anencapsulating agent, a binder, an emulsifier, a dye, a UV protective, abuffer, a flow agent, a fertilizer, a nitrogen fixation agent,micronutrient donors, or other preparations that influence plant growth.The agricultural composition can also include one or more agrochemicalsincluding: herbicides, insecticides, fungicides, bactericides,nematicides, molluscicides, acaracides, plant growth regulators, harvestaids, and fertilizers, which can also be combined with carriers,surfactants or adjuvants as appropriate for the agrochemical. Suitablecarriers and adjuvants can be solid or liquid and correspond to thesubstances ordinarily employed in formulation technology, e.g., naturalor regenerated mineral substances, solvents, dispersants, wettingagents, tackifiers, binders, or fertilizers. The active ingredients ofthe present disclosure are normally applied in the form of compositionsand can be applied to the crop area, plant, or seed to be treated. Forexample, the compositions of the present disclosure may be appliedduring growth, seeding or storage.

Surface-active agents that can be used with the presently describedcompounds include anionic compounds such as a carboxylate of, forexample, a metal; carboxylate of a long chain fatty acid; anN-acylsarcosinate; mono- or di-esters of phosphoric acid with fattyalcohol ethoxylates or salts of such esters; fatty alcohol sulfates suchas sodium dodecyl sulfate, sodium octadecyl sulfate or sodium cetylsulfate; ethoxylated fatty alcohol sulfates; ethoxylated alkylphenolsulfates; lignin sulfonates; petroleum sulfonates; alkyl aryl sulfonatessuch as alkyl-benzene sulfonates or lower alkylnaphtalene sulfonates,e.g., butyl-naphthalene sulfonate; salts of sulfonatednaphthalene-formaldehyde condensates; salts of sulfonatedphenol-formaldehyde condensates; more complex sulfonates such as theamide sulfonates, e.g., the sulfonated condensation product of oleicacid and N-methyl taurine; or the dialkyl sulfosuccinates, e.g., thesodium sulfonate or dioctyl succinate. Non-ionic agents includecondensation products of fatty acid esters, fatty alcohols, fatty acidamides or fatty-alkyl- or alkenyl-substituted phenols with ethyleneoxide, fatty esters of polyhydric alcohol ethers, e.g., sorbitan fattyacid esters, condensation products of such esters with ethylene oxide,e.g., polyoxyethylene sorbitar fatty acid esters, block copolymers ofethylene oxide and propylene oxide, acetylenic glycols such as2,4,7,9-tetraethyl-5-decyn-4,7-diol, or ethoxylated acetylenic glycols.Examples of a cationic surface-active agent include, for instance, analiphatic mono-, di-, or polyamine such as an acetate, naphthenate oroleate; or oxygen-containing amine such as an amine oxide ofpolyoxyethylene alkylamine; an amide-linked amine prepared by thecondensation of a carboxylic acid with a di- or polyamine; or aquaternary ammonium salt.

Examples of inert materials that can be used with the presentlydescribed compounds include, but are not limited to, inorganic mineralssuch as kaolin, phyllosilicates, carbonates, sulfates, phosphates, orbotanical materials such as cork, powdered corncobs, peanut hulls, ricehulls, and walnut shells.

Herbicides that can be used with the presently described compoundsinclude compounds that kill or inhibit growth or replication of plants,typically a subset of plants that is distinct from the desired plant orcrop. There are several modes of action: ACCase inhibition, carotenoidbiosynthesis inhibition, cell wall synthesis inhibition, ALS inhibition,ESP synthase inhibition, glutamine synthase inhibition, HPPD inhibition,microtubule assembly inhibition, PPO inhibition, etc. Examples ofcommercially available herbicides include One-Time®, MSMA, Corvus®,Volunteer®, Escalade®, Q4®, Raptor®, Acumen®, Sencor®, Bullet®,TopNotch®, Valor®, PastureGard®, glycophosate (Roundup®), DSMA,Break-Up®, Hyvar®, Barricade®, etc. Herbicides can be mixed with“herbicide safeners” to reduce general toxicity of the herbicide, asdescribed, e.g., in Riechers et al. (2010) Plant Physiol. 153:3.

Pesticides (e.g., nematicides, molluscicides, insecticides,miticide/acaricides) can be used in combination with the presentlydisclosed compounds to kill or reduce the population of undesirablepests affecting the plant. Pesticides can also be used with repellantsor pheromones to disrupt mating behavior. Insectides are directed toinsects, and include, e.g., those of botanical origin (e.g., allicin,nicotine, oxymatrine, jasmolin I and II, quassia, rhodojaponin III, andlimonene), carbamate insecticides (e.g., carbaryl, carbofuran,carbosulfan, oxamyl, nitrilacarb, CPMC, EMPC, fenobucarb), fluorineinsecticides, formamidine insecticides, fumigants (e.g., ethylene oxide,methyl bromide, carbon disulfide), chitin synthesis inhibitors,macrocyclic lactone insecticides, neonicotinoid insecticides,organophosphate insectides, urea and thiourea insectides, etc.Nematicides affect nematodes, and include, e.g., organophosphorusnematicides (e.g., diamidafos, fosthiazate, heterophos, phsphamidon,triazophos), fumigant nematicides (e.g., carbon disulfide, methylbromide, methyl iodide), abamectin, carvacrol, carbamate nematicides(e.g., benomyl, oxamyl), etc. Molluscicides are directed to slugs andsnails, and include, e.g., allicin, bromoacetamide, thiocarb,trifenmorph, fentin, copper sulfate, etc. Many pesticides target morethan one type of pest, so that one or two can be selected to targetinsects, mollusks, nematodes, mitogens, etc.

Fertilizers typically provide macro- and micronutrients in a form thatthey can be utilized by the plant, or a plant-associated organism. Theseinclude, e.g., nitrogen, phosphorus, potassium, sulfur, calcium,potassium, boron, chlorine, copper, iron, manganese, molybdenum, zinc,nickel, and selenium. Fertilizers are often tailored to specific soilconditions or for particular crops or plants. Fertilizers that can beused with the presently described compounds include naturally-occurring,modified, concentrated and/or chemically synthesized materials, e.g.,manure, bone meal, compost, fish meal, wood chips, etc., or can bechemically synthesized, UAN, anhydrous ammonium nitrate, urea, potash,etc. Suppliers include Scott®, SureCrop®, BCF®, RVR®, Gardenline®, andmany others known in the art.

Fungicides are compounds that can kill fungi or inhibit fungal growth orreplication. Fungicides that can be used with the presently disclosedcompounds include contact, translaminar, and systemic fungicides.Examples include sulfur, neem oil, rosemary oil, jojoba, tea tree oil,Bacillus subtilis, Ulocladium, cinnamaldehyde, etc.

The compositions of the disclosure can be in a suitable form for directapplication or as a concentrate of primary composition that requiresdilution with a suitable quantity of water or other diluant beforeapplication. The concentration of a compound of Formula I will varydepending upon the nature of the particular formulation, specifically,whether it is a concentrate or to be used directly, and the type ofplant and pathogen.

VII. Methods for Treating a Plant

The presently described compounds can be applied to the environment of aplant or plant pathogen by, for example, spraying, atomizing, dusting,scattering, coating or pouring, introducing into or on the soil,introducing into irrigation water, by seed treatment or generalapplication or dusting at the time when the pathogen has begun to appearor before the appearance of pathogens as a protective measure. Typicallypathogen control is contemplated early in plant growth, as this is thetime when the plant can be most severely damaged. The compositions ofthe disclosure can conveniently contain an insecticide if this isthought necessary.

The presently described compounds can be applied simultaneously or insuccession with other compounds. Methods of applying an activeingredient or agricultural composition of the present disclosure thatcontains at least one compound of Formula I include, but are not limitedto, foliar application (e.g., spray or soak), seed coating, and soilapplication. The number of applications and the rate of applicationdepend on desired use, e.g., pathogen protection or increased growth,and conditions, e.g., the intensity of pathogen infestation or growingconditions.

The examples and embodiments described herein are for illustrativepurposes only, and various modifications or changes are to be includedwithin the spirit and purview of this application and scope of theappended claims. All patents, patent applications, internet sources, andother published reference materials cited in this specification areincorporated herein by reference in their entireties.

VIII. Examples A. Example 1: PMPs are Small Molecule Elicitors ofCaBP22⁻³³³::GUS Expression

We took a chemical genomics-based approach to identify new syntheticelicitors for the plant immune system and develop environmentally safepesticides. By high-throughput chemical screening of commerciallyavailable chemical libraries, we identified drug-like organic compoundsthat induce the pathogen-responsive pCaBP22⁻³³³::GUS reporter gene intransgenic Arabidopsis. We reported one of them,3-5-dicholoroanthranlilic acid (DCA) in Knoth et al. (2009) PlantPhysiol. 150:333. DCA triggered fast, strong and transient diseaseresistance against as the pathogenic oomycete Hyaloperonosporaarabidopsidis (Peronospora) and the bacterial pathogen Pseudomonassyringae. DCA activity was shown in various Arabidopsis defense mutantsto be partially dependent on the WRKY70 transcription factor, incontrast to INA and BTH, which are fully dependent on thetranscriptional co-factor.

The PMPs shown in FIG. 1A were also selected from the compoundsidentified in the reporter assay screen. The PMPs were selected from theChemBridge DIVERSet™ library. These compounds have not been reported assynthetic elicitors, and have chemical structures distinct from DCA(see, e.g., US20110301035) or any other known plant defense inducer.

B. Example 2: CMP199 Causes Rapid and Transient Resistance to Peronopora

CMP199 (FIG. 1A) was selected for further study to determine whetherCMP199 could induce pathogen resistance in soil-grown plants. Col-0sprayed with CMP199 concentrations as low as 1 μM prior to infectionwith the virulent Peronospora isolate Noco2 exhibited significantlyreduced numbers of Noco2 spores 7 days post infection (dpi). Todetermine if CMP199 differs from other synthetic elicitors, Col-0seedlings were treated with DCA or HTC at the indicated concentrationsand compared. CMP199 inhibits Noco2 spores at a much lower concentrationthan DCA or HTC (FIG. 1B).

1.-23. (canceled)
 24. An agricultural composition comprising thecompound of Formula I

or a salt thereof, wherein: R², R³, R⁴, R⁶, R⁸, and R¹⁰ are eachindependently selected from hydrogen, halogen, hydroxyl, alkoxyl, nitro,substituted or unsubstituted amino, unsubstituted alkyl, substituted orunsubstituted alkenyl, and substituted or unsubstituted carbonyl; R¹ andR⁵ are each independently selected from hydrogen, hydroxyl, alkoxyl,nitro, substituted or unsubstituted amino, substituted or unsubstitutedalkyl, substituted or unsubstituted alkenyl, and substituted orunsubstituted carbonyl; and R⁷ and R⁹ are each independently selectedfrom hydrogen, hydroxyl, alkoxyl, nitro, substituted or unsubstitutedamino, unsubstituted alkyl, substituted or unsubstituted alkenyl, andsubstituted or unsubstituted carbonyl, wherein, when contacted with aplant, the compound increases pathogen resistance or growth of the plantcompared to pathogen resistance or growth of a control plant notcontacted with the compound.
 25. The agricultural composition of claim24, wherein: R², R³, R⁴, R⁶, R⁸, and R¹⁰ are each independently selectedfrom hydrogen, halogen, hydroxyl, alkoxyl, nitro, substituted orunsubstituted amino, and unsubstituted alkyl, substituted orunsubstituted alkenyl; R¹ and R⁵ are each independently selected fromhydrogen, hydroxyl, alkoxyl, nitro, substituted or unsubstituted amino,substituted or unsubstituted alkyl, and substituted or unsubstitutedalkenyl; and R⁷ and R⁹ are each independently selected from hydrogen,hydroxyl, alkoxyl, nitro, substituted or unsubstituted amino,unsubstituted alkyl, and substituted or unsubstituted alkenyl.
 26. Theagricultural composition of claim 25, wherein R¹ and R⁵ are eachindependently selected from hydrogen and hydroxyl.
 27. The agriculturalcomposition of claim 25, wherein R² and R⁴ are each independentlyselected from hydrogen and halogen.
 28. The agricultural composition ofclaim 25, wherein R¹ is hydroxyl.
 29. The agricultural composition ofclaim 25, wherein R⁵ is hydrogen.
 30. The agricultural composition ofclaim 25, wherein R² and R⁴ are both halogen.
 31. The agriculturalcomposition of claim 26, wherein R² and R⁴ are each independentlyselected from hydrogen and halogen.
 32. The agricultural composition ofclaim 31, wherein R¹ is hydroxyl.
 33. The agricultural composition ofclaim 32, wherein R⁵ is hydrogen.
 34. The agricultural composition ofclaim 33, wherein R² and R⁴ are both chlorine.
 35. An agriculturalcomposition comprising the compound of Formula I

or a salt thereof, wherein: R¹ and R⁵ are each independently selectedfrom hydrogen, hydroxyl, alkoxyl, nitro, substituted or unsubstitutedamino, substituted or unsubstituted alkyl, substituted or unsubstitutedalkenyl, and substituted or unsubstituted carbonyl; R² and R⁴ are eachindependently selected from halogen, hydroxyl, alkoxyl, nitro,substituted or unsubstituted amino, substituted or unsubstituted alkyl,substituted or unsubstituted alkenyl, and substituted or unsubstitutedcarbonyl; R³ is selected from hydrogen, halogen, hydroxyl, alkoxyl,nitro, substituted or unsubstituted amino, substituted or unsubstitutedalkyl, substituted or unsubstituted alkenyl, and substituted orunsubstituted carbonyl; and R⁶, R⁷, R⁸, R⁹ and R¹⁰ are eachindependently selected from hydrogen, halogen, hydroxyl, alkoxyl, nitro,substituted or unsubstituted amino, unsubstituted alkyl, substituted orunsubstituted alkenyl, and substituted or unsubstituted carbonyl,wherein, when contacted with a plant, the compound increases pathogenresistance or growth of the plant compared to pathogen resistance orgrowth of a control plant not contacted with the compound.
 36. Theagricultural composition of claim 35, wherein: R¹ and R⁵ are eachindependently selected from hydrogen, hydroxyl, alkoxyl, nitro,substituted or unsubstituted amino, substituted or unsubstituted alkyl,and substituted or unsubstituted alkenyl; R² and R⁴ are eachindependently selected from halogen, hydroxyl, alkoxyl, nitro,substituted or unsubstituted amino, substituted or unsubstituted alkyl,and substituted or unsubstituted alkenyl; R³ is selected from hydrogen,halogen, hydroxyl, alkoxyl, nitro, substituted or unsubstituted amino,substituted or unsubstituted alkyl, and substituted or unsubstitutedalkenyl; and R⁶, R⁷, R⁸, R⁹ and R¹⁰ are each independently selected fromhydrogen, halogen, hydroxyl, alkoxyl, nitro, substituted orunsubstituted amino, unsubstituted alkyl, and substituted orunsubstituted alkenyl.
 37. The agricultural composition of claim 36,wherein R¹ is hydroxyl.
 38. The agricultural composition of claim 37,wherein R⁵ is hydrogen, hydroxyl, or part of a phenyl group with R⁴. 39.The agricultural composition of claim 37, wherein R⁴ is halogen,hydroxyl, or part of a phenyl group with R⁵.
 40. The agriculturalcomposition of claim 37, wherein R² and R⁴ are both halogen.
 41. Theagricultural composition of claim 40, wherein R⁷ and R⁹ are bothhalogen.
 42. An agricultural composition comprising the compound ofFormula I

or a salt thereof, wherein: R¹, R³, R⁵, R⁶, R⁷, R⁸, R⁹, and R¹⁰ are eachindependently selected from hydrogen, halogen, hydroxyl, alkoxyl, nitro,substituted or unsubstituted amino, unsubstituted alkyl, substituted orunsubstituted alkenyl; and R² and R⁴ are each independently selectedfrom hydrogen, hydroxyl, alkoxyl, nitro, substituted or unsubstitutedamino, substituted or unsubstituted alkyl, substituted or unsubstitutedalkenyl, and substituted or unsubstituted carbonyl, wherein, whencontacted with a plant, the compound increases pathogen resistance orgrowth of the plant compared to pathogen resistance or growth of acontrol plant not contacted with the compound.
 43. The agriculturalcomposition of claim 42, wherein: R¹, R³, R⁵, R⁶, R⁷, R⁸, R⁹, and R¹⁰are each independently selected from hydrogen, halogen, hydroxyl,alkoxyl, nitro, substituted or unsubstituted amino, unsubstituted alkyl,substituted or unsubstituted alkenyl; and R² and R⁴ are eachindependently selected from hydrogen, hydroxyl, alkoxyl, nitro,substituted or unsubstituted amino, substituted or unsubstituted alkyl,and substituted or unsubstituted alkenyl.